|Publication number||US7268977 B2|
|Application number||US 10/779,356|
|Publication date||Sep 11, 2007|
|Filing date||Feb 12, 2004|
|Priority date||Feb 12, 2004|
|Also published as||US20050180057|
|Publication number||10779356, 779356, US 7268977 B2, US 7268977B2, US-B2-7268977, US7268977 B2, US7268977B2|
|Inventors||James M. Freitag, Mustafa M. Pinarbasi|
|Original Assignee||Hitachi Global Storage Technologies Netherlands B.V.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (17), Referenced by (4), Classifications (12), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to a magnetoresistive spin valve sensor, and in particular to a self-pinned spin valve sensor with a capping layer structure that provides high compressive stress.
A magnetic head assembly typically includes write and read heads wherein the write head writes magnetic bits of information into a rotating magnetic disk in a disk drive and the read head reads the magnetic bits of information from the rotating disk. The magnetic head assembly is typically located on a slider that “flies” over a rotating magnetic disk on a cushion of air between the disk surface and the air bearing surface of the slider.
The read head typically includes a spin valve sensor and two lead layers that are connected to the side edges of the spin valve sensor through which a sense current is conducted. The spin valve sensor and leads are located between a pair of nonmagnetic electrically insulative gap layers and a pair of ferromagnetic shield layers.
In general, a spin valve sensor has a pinned ferromagnetic structure in close proximity to a free ferromagnetic layer. The direction of magnetization in the pinned ferromagnetic structure is fixed or “pinned”, in a specified direction. Some spin valve sensors use an adjoining antiferromagnetic layer to pin the direction of the pinned ferromagnetic structure and some spin valve sensors use self-pinned ferromagnetic structures, which do not use an antiferromagnetic pinning layer. A self-pinned ferromagnetic layer typically includes two ferromagnetic layers that provide large coercivity and a strong anitstropy field that obviate the antiferromagnetic pinning layer.
The direction of magnetization in the free layer is responsive to the external magnetic field to which the read element is subjected. The magnetization in the free layer is usually partially stabilized with adjacent permanent magnets. The relative directions of the magnetization in the pinned layer and the free layer determines the resistance of the read element.
In a self-pinned sensor design, the magnetic anisotropy caused by the positive magnetostriction of the pinned layers together with a compressive film stress aligns the magnetization of the pinned layers in a direction perpendicular to the air bearing surface of the slider, which is the desired state for a spin valve. The anisotropy field Hk for a given magnetostriction λ and film stress σ is given by the equation:
where M is the saturation moment of the pinned layers. To increase the pinning field Hk in the pinned layers, it is desirable to increase the compressive stress σ of the film.
The use of a metal capping layer provides a large compressive stress. For a capping layer of a thickness t and with stress σ′, the bending moment exerted by the capping layer on the underlying sensor layers, which causes a stress to develop in these layers, will be proportional to the force per unit width (F/w) of the capping layer:
F/W=σ′*t eq. 2
which is proportional to the thickness of the film. Thus, one method to further increase the pinning field Hk in the pinned layers is to use a thicker capping layer. A thicker capping layer will produce larger bending moments and, consequently, more stress in the underlying sensor. Unfortunately, by increasing the thickness of a metallic capping layer, more sense current is shunted by the capping layer, which leads to a significant decrease in sensor performance. Further, significantly increasing the thickness of the capping layer is undesirable because of the increase in sensor size.
Accordingly, what is needed is an improved capping layer with a large compressive stress and high electrical resistivity.
A capping layer, in accordance with an embodiment of the present invention, includes a first capping layer, formed from a refractory metal, and a second capping layer formed from silicon. The interface between the refactory metal layer and the silicon layer form a silicide that provides a large compressive stress on the underlying spin valve sensor. The compressive stress, advantageously, increases the pinning field in the self-pinned pinned layer structure, while providing a high resistivity so that less sense current is shunted by the capping layer structure compared to an all metal capping layer structure that provides a comparable compressive stress.
In one embodiment of the present invention, a spin valve sensor includes a ferromagnetic free layer structure, a ferromagnetic pinned layer structure, and a nonmagnetic spacer layer located between the free layer structure and the pinned layer structure. The spin valve sensor also includes a capping layer structure including a refractory metal layer and a silicon layer, wherein the refractory metal layer is disposed between the free layer structure and the silicon layer.
In another embodiment of the present invention, an apparatus includes a spin valve sensor, the spin valve sensor includes a ferromagnetic free layer structure, a ferromagnetic pinned layer structure, and a nonmagnetic electrically conductive spacer layer located between the free layer structure and the pinned layer structure. The spin valve sensor further includes a capping layer structure comprising a first capping layer a second capping layer, the first capping layer located between the second capping layer and the pinned layer structure, the first capping layer interfacing with the second capping layer to form a silicide that provides a compressive stress on the pinned layer structure.
In another embodiment of the present invention, a method of making a spin valve sensor for a magnetic head assembly includes forming a pinned layer structure, forming a nonmagnetic electrically conductive spacer layer on the pinned layer structure, and forming a ferromagnetic free layer structure on the spacer layer. The method includes forming a capping layer structure by forming a first capping layer of a refractory metal, and forming a second capping layer of silicon on the first capping layer, wherein the first capping layer is located between the pinned layer structure and the second capping layer structure, and wherein a silicide is formed at the junction of the first capping layer and the second capping layer.
In accordance with an embodiment of the present invention, a capping layer structure is used to enhance the compressive stress of a self-pinned spin valve sensor that may be used in a magnetic disk drive or similar type of device.
The sensor 210 includes a pinned layer structure 212, a free layer structure 214 and a spacer layer 216 there between. The pinned layer structure 212 includes a coupling layer 218 between a first and second antiparallel pinned layers 220 and 222. The pinned layers 220 and 222 are ferromagnetic layers with magnetic moments 220 a, and 222 a, which are out of and into the sensor 210, respectively, i.e., normal to the air bearing surface of the slider. The pinned layer structure 212 is deposited over seed layered 224, 226 and 228.
The free layer structure 214 includes first and second free ferromagnetic layers 230 and 232. The free layer structure 214 has a magnetic moment 214 a that is parallel to the air bearing surface of the slider. When a signal from the rotating magnetic disk rotates the magnetic moment 214 a of the free layer structure into the sensor, the magnetic moments 220 a and 222 a become more antiparallel, which increases the resistance of the sensor, and when the signal field from the rotating magnetic disk rotates the magnetic moment 214 a of the free layer structure out of the sensor, the magnetic moments 220 a and 222 a become more parallel, which decreases the resistance of the sensor. By measuring and processing the changes in resistance in the sensor by passing a sense current through the sensor, the data on the disk can be determined.
A capping layer structure 240, in accordance with an embodiment of the present invention, is then formed over the free layer structure 214. The capping layer structure 240 includes at least two layers that enhance the compressive stress of the sensor. The capping layer structure 240 includes a layer 242 of a refractory metal, such as ruthenium, molybdenum, tungsten, tantalum, niobium, chromium, vanadium and rhenium, over which is deposited a layer 244 of silicon. The capping layer structure 240 may also include an underlying protective metal layer 246, such as tantalum. The refractory metal layer 242 and silicon layer 244 may be deposited by conventional means, such as plasma vapor deposition and/or sputtering.
Table 1 provides exemplary materials and thickness for the layers of the sensor 210.
It should be understood that the materials and thickness provided in Table 1 are merely exemplary. Alternative materials and thicknesses may be used if desired. For example, the refractory metal layer 242 and silicon layer 244 may have a thickness range of 5 Å to 30 Å. Moreover, additional or fewer layers may be included in the sensor if desired.
The deposition of the silicon layer 244 on the refractory metal layer 242 forms a silicide, illustrated in
Thus, the use of a silicon layer 244 deposited over the refractory metal layer 242, in accordance with an embodiment of the present invention produces a large compressive stress due to the formation of the silicide 245. Moreover, the resulting structure also has a high resistivity. Consequently, the capping layer structure 240 will shunt less sense current while providing increased compressive stress, which advantageously increases the pinning field Hk as described in equation 1.
Although the present invention is illustrated in connection with specific embodiments for instructional purposes, the present invention is not limited thereto. Various adaptations and modifications may be made without departing from the scope of the invention. For example, different refractory metals and layer thicknesses may be used in the capping layer structure. Moreover, the structure and thicknesses of the spin valve sensor may vary as desired. Further, different types of spin valve sensors may be used with the capping layer structure. For example, the spin valve sensor may use an antiferromagnetic pinning layer for pinning the magnetic moment of the pinned layer structure. Further, the capping layer structure may be used with a top spin valve sensor, i.e., a sensor with the pinned layer structure disposed between the free layer structure and the capping layer structure. Therefore, the spirit and scope of the appended claims should not be limited to the foregoing description.
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|U.S. Classification||360/324.1, G9B/5.117|
|International Classification||G11B5/127, G11B5/39, G11B5/33|
|Cooperative Classification||G11B2005/3996, B82Y10/00, B82Y25/00, G11B5/3906|
|European Classification||B82Y10/00, B82Y25/00, G11B5/39C1|
|Feb 12, 2004||AS||Assignment|
Owner name: HITACHI GLOBAL STORAGE TECHNOLOGIES NETHERLANDS B.
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:FREITAG, JAMES M.;PINARBASI, MUSTAFA M.;REEL/FRAME:014998/0998
Effective date: 20040210
|Mar 1, 2011||FPAY||Fee payment|
Year of fee payment: 4
|Oct 25, 2012||AS||Assignment|
Owner name: HGST, NETHERLANDS B.V., NETHERLANDS
Free format text: CHANGE OF NAME;ASSIGNOR:HGST, NETHERLANDS B.V.;REEL/FRAME:029341/0777
Effective date: 20120723
Owner name: HGST NETHERLANDS B.V., NETHERLANDS
Free format text: CHANGE OF NAME;ASSIGNOR:HITACHI GLOBAL STORAGE TECHNOLOGIES NETHERLANDS B.V.;REEL/FRAME:029341/0777
Effective date: 20120723
|Apr 24, 2015||REMI||Maintenance fee reminder mailed|